Position sensors are commonly used to measure the position of various elements of a movable mechanical system. Such systems often include one or more actuators, which typically include a motor and output drive train, to provide the desired linear or rotary motion. These actuators are commonly electromagnetic, piezoelectric, pneumatic, and hydraulic actuators. These systems may also include position feedback sensors and circuitry as part of the associated actuator system, and may be referred to as servoactuators or servocontrol systems.
Position sensors for mechanical systems typically measure the displacement of an element of an actuator or a component moved by such an element. In some systems, magnetic sensors are used as to sense the position of the desired components. Two classes of such magnetic sensors are Hall effect sensors and magneto-resistive sensors. Hall effect sensors measure a voltage that is induced in a semiconductor material due to the effect of a magnetic field on an electrical current flowing in the semiconductor material, known as a Hall voltage. Hall effect sensors are sometimes referred to as Hall effect elements or Hall effect devices (HEDs). Magneto-resistive sensors utilize materials that exhibit a change in resistance due to the influence of a magnetic field.
One class of Hall effect sensors include digital Hall effect sensors, which typically provide a binary output that is dependent upon the presence, absence, and/or orientation of a magnetic field. The binary output, also known as the digital Hall state, can be counted and used to indicate the movement of the component of interest that the one or more magnets are coupled to. In this way, the movement and position of a servoactuator component of interest may be determined. Digital Hall effect devices typically include signal-conditioning circuitry, e.g., a Schmitt inverter, to condition the output signal of an analog HED.
Limitations exist with current techniques of sensing position with magnetic sensors. Such limitations may be particularly pronounced in movable mechanical systems having complex drive trains. Inaccurate position measurement can occur when individual magnetic sensors are subject to ambient environmental factors such a temperature variations, local magnetic field variations, and electromagnetic interference or noise. Calibration errors in the sensors may also produce or contribute to errors in position measurement.
Inaccurate position measurement can occur in movable mechanical systems, including those with complex drive trains, when one or more magnetic sensors are used to measure a single mechanical element that is subject to back lash or mechanical compliance. For example, backlash and mechanical compliance are not accommodated in a complex drive train by a magnetic sensor used to measure the rotation of an EMA motor shaft used as a prime mover for the drive train.